State resolved rotational excitation in HD+D2 collisions. I. Angular dependence of 0→1 transitions

Abstract

In a crossed molecular beam experiment, time‐of‐flight distributions of HD molecules scattered from D₂ have been measured at 42.2, 45.4, and 50.8 meV collision energy using the pseudorandom chopper method. In all cases rotational transitions of HD from j=0 to j=1 were resolved. At 45.4 meV complete differential cross sections have been generated from 10 ° to 120 °. They display well resolved diffraction oscillations in both the elastic 0→0 and inelastic 0→1 channels. Calculations show that these data essentially provide information on the position and the slope of the isotropic H₂–H₂ interaction potential near the zero point. The comparison between measurement and close coupling calculations based on the ab initio potential surface of Meyer and Schaefer shows a remarkable agreement. Only very small deviations in the positions of the diffraction oscillation extrema occur giving rise to a slight modification of the repulsive wall near the zero point. It has to be shifted by 0.1 Å to give a perfect fit to the measured data.